Abstract: Inclined tube is the conveying pipe for catalyst circulation in FCC unit. Catalyst flowing smoothly in the pipe is one of the key points for the steady operation of the device. The fluidized states of the catalyst and gas in the inclined tube of a 3.3 Mt/a FCCU were analyzed by measuring the axial pressure profiles of the regenerator inclined tube and the catalyst apparent density in front of the slide valve. The result showed that the dense-phase flow was formed in the lower part of the pipe, resulting in a significantly increased friction pressure drop, which is the main cause for the reversal of axial pressure distribution. Inclined tube operation was divided into three parts according to the direction of gas flow: Part I was the negative pressure differential degassing region; Part II was the negative pressure differential gas holding region; Part III was the positive pressure differential gas holding region. The fluidized state of catalyst can be changed by adjusting aeration rate.

Key words: catalytic cracking, regenerator inclined tube, fluidized state, aeration, pressure, density